This invention relates to the dimerization of olefins in a loop reactor. In another aspect, this invention relates to the dimerization of olefins in a loop reactor that has a flash zone located within the loop thereby allowing the product to be removed as a vapor from the flash. In another aspect, this invention relates to the dimerization of olefins wherein two flashing zones are used to remove the product as a vapor. In still another aspect, this invention relates to the concentration of a nonvolatile homogeneous catalyst for subsequent recycling of catalyst to the reactor loop by flashing off product. In yet another aspect, this invention relates to a dimerization process of olefins wherein product heavies are used as an absorbent in an absorber. in still another aspect, the invention is concerned with the use of product heavies to absorb unreacted olefin and recycle the olefin to the loop reactor in a dimerization process. In still another aspect, this invention relates to a dimerization process in which dimer product is utilized as an absorbent for unreacted ethylene. The invention also relates to a dimerization process for olefins in a loop reactor in which a vapor-liquid contact device is contained within the loop and dimer product is used as an absorbent for unreacted ethylene within the device. The invention is also concerned with the use of the vapor-liquid contacting device contained within the loop of a loop reactor for low-concentration olefin feeds. In still another aspect, this invention relates to a dimerization process for olefins in a thermosiphon loop reactor using the energy of the feed gas to induce reactor circulation. This invention also relates to the use of a thermosiphon loop reactor in order to dimerize olefins in a low-concentration feed.
Another aspect of this invention relates to the apparatus used to dimerize olefins. in one aspect, the invention relates to olefin dimerization apparatus comprising a flashing means in the continuous loop of a loop reactor. In another aspect, this invention relates to olefin dimerization apparatus comprising two flashing means. In another aspect, this invention relates to olefin dimerization apparatus comprising a vapor-liquid contactor in the continuous loop of a loop reactor. In still another aspect, this invention relates to olefin dimerization apparatus comprising a thermosiphon loop reactor.
The dimerization of olefins is a well-known process in the art, e.g., U.S. Pat. No. 3,631,121 and U.S. Pat. No. 3,485,881. Olefin dimerization processes are applicable to olefins in general, however, dimerization is an especially attractive method for producing butylenes from ethylene for subsequent use in alkylation, dehydrogenation to butadiene and other chemical processes. Problems arise in dimerization processes, however, in that the process suffers from low selectivity to the dimer with much of the feed being converted to trimers and product heavies. It is known that selectivity can be improved by using shorter reactor residence time, but the disadvantages of this approach are low ethylene conversion and low catalyst productivity.
Other problems arise when the feed stream is low in olefin concentration, e.g. only a small amount of ethylene with the remainder of the feed stream being gases such as hydrogen, methane, ethane, etc. It would be desirable to remove the ethylene from the gas before the gas ends up as a fuel gas stream. The amount of olefin, e.g., ethylene, is so small, however, that it would be economically undesirable to use conventional equipment with the expensive power requirements of circulating the reaction medium through the loop reactor as well as costly recompression and the expense of a low temperature olefin recovery column.
Accordingly, it is an object of this invention to provide an improved and more economical process for olefin dimerization.
Another object of this invention is to provide an olefin dimerization process with improved olefin selectivity and conversion as well as catalyst productivity.
Another object of this invention is to provide an olefin dimerization process which recycles the olefin reactant yet avoids costly recompression and an expensive low temperature recovery column.
Another object is to provide a method for dimerizing an olefin from a low concentration stream to thereby obviate the need for olefin purification facilities.
Still another object of the invention is to minimize the power requirements of an olefin dimerization process using a loop reactor.
Other aspects, objects and advantages are apparent from a study of this disclosure, the drawings and the appended claims.